We have extended the use of finer 24 mesh polypropylene screen to larger sizes of vent caps.  This has been a manufacturing challenge in the past and in the past we used 10×10 mesh.  Lately however the EPA hs issued guidance on potable water storage tanks and recommends 24 mesh screen. However now we offer all sizes up to 6 inches with this mesh.  The 24 mesh prevents entry fo mosquitoes which is a must for tanks that hold water.    More information on our vent cap page.